Field of the Invention
The present invention relates to pneumatic apparatus of the percussive type used in construction, mining, mechanical engineering and metallurgy and has specific reference to single-stroke pneumatic apparatus.
Description of the Prior Art
Single-stroke pneumatic apparatus commonly employed for marking, centre-pricking, marking-off and chiselling off risers are pneumatic hammers. The tool the hammer is fitted with varies with the application. It can be a stamp, a prick-punch, a hobby or a chisel. The tool is supported in a hollow frame with inlet and outlet ports and a striker dividing the frame bore into forward- and working-stroke chambers. A directional flow control is provided on the frame. The source of energy is compressed air fed from a mobile or stationary compressor over a flexible hose. In operation, the compressed air admitted into the chambers of the frame with the aid of the directional flow control manipulated by the operator, causes the striker to reciprocate back and forth axially and deliver cyclewise blows at the end face of the tool. The work done by the tool materializes in any of the following operations depending on the type of the tool: marking, centre-pricking, chiselling or riveting.
The atmosphere at the working place where pneumatic hammers are in use is commonly laden with dust and the operator cannot but stay in such a surrounding. Therefore, the problem of increasing the reliability of the pneumatic hammer is one of great concern.
Known in the art is a single-stroke pneumatic apparatus (cf. USSR Inventor's Certificate No. 781048, IPC B25D 9/14, 1980) comprising a hollow cylindrical frame provided with inlet and outlet ports, and a striker recurrently interacting with a resilient means located at an end face of the frame. The directional flow control is a solenoid-actuated valve operated by a microswitch. The valve made up of three parts lacking a mechanical link with each other is of intricate design. Apart from that, the known apparatus lacks reliability, for dust and other fine particles are sucked into the bore of the frame through the outlet ports when the striker is on a back stroke. The noisy high-velocity exhaust from the apparatus creates trying labour conditions for the operator.
Also known is a single-stroke pneumatic apparatus, i.e. a pneumatic hammer (cf. German Patent No. 671,958, Cl. 87b 2/11, 1939) comprising a hollow cylindrical frame with inlet and outlet ports, a spring-loaded striker forming forward- and back-stroke chambers in the frame bore, a handgrip located wherein is a directional flow control and a tool fixed in the upper end of the frame.
In the known apparatus, the outlet ports are laid out in a way which cannot prevent ingress of dust-laden atmosphere into the frame bore. Therefore, the hammer cannot last long. The noisy exhaust from the apparatus creates trying labour conditions for the operator.